This article was taken from the October 2013 issue of Wired magazine. Be the first to read Wired's articles in print before they're posted online, and get your hands on loads of additional content by <span class="s1">subscribing online.

A few years ago, I had dinner with friends. It was several notches above the usual. The jokes were funnier; even the food tasted better.

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Why? The secret was not the addition of a new ingredient, but the removal of an old one: my smartphone.

Earlier that afternoon, I had the misfortune of dropping it in the bathroom. Don't ask where: suffice to say, I am no longer using that phone. Its absence had a subtle effect on dinner that evening.

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Even though I would not have used it during dinner, I would have used it beforehand: I would have inevitably checked my email on the way there. I might have read about some project that was running out of cash, or some deadline that was slipping. These emails would have followed me to dinner. Like a needy companion, they would have constantly intruded. My mind would have zigzagged between the conversation and the flavours of the food and my messages. Only a part of me would have been at that meal. By now most of us appreciate the hubris of multitasking. My dinner experience illustrates a different, under-appreciated challenge: serial tasking.

Serial tasking is hard because switching tasks is hard, even when the tasks are easy and similar. In some experiments, bilingual speakers are asked to read out numbers, first in one language and then midway in another language. They often stumble at the switch, taking many tries before they hit their stride again. This is not a lack of familiarity: shifting from a foreign language to the mother tongue is particularly hard. Task switching is hard because we do not control what is on our mind. Despite our efforts, the original task continues to occupy our mental bandwidth. Although we can control where our time goes, we cannot fully control how our bandwidth is allocated.

We become less and less productive exactly when we need to be most productiveKeepInline

This is easy to overlook. Many of us arrange our calendars as we might arrange the inside of a refrigerator: we look for empty space where that next meeting can be squeezed in. Yet our minds do not work that way. Working out a key piece of your new strategy does not just require time, it requires bandwidth. You may have found time for it on your calendar, right after that meeting about your startup's finances. But you have not found the bandwidth for it: your tight finances will still be occupying your mind. We ought to arrange calendars as we arrange art on our walls and ask: how does this task fit next to the surrounding ones?

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The experiment on language-switching in fact understates the problem, as Eldar Shafir and I show in our book Scarcity: Why Having Too Little Means So Much. Sitting at dinner, that email about a pressing deadline calls out the loudest. This is no coincidence: thoughts of scarcity (in this case not having enough time) impose themselves most strongly. This means serial tasking is hardest when we are busiest, which unfortunately is also when we serial-task most heavily. Faced with a time shortage, we squeeze tasks into the nooks and crannies of our calendar, leaving less and less time to switch between them. As a result, we become less and less productive exactly when we need to be most productive. When we are most busy, we think we are becoming better users of time when we are really becoming worse managers of our bandwidth.

Now, if you'll excuse me, with this deadline now finished, I'm off to a nice, quiet dinner party.

Sendhil Mullainathan is a professor of economics at Harvard University, and the cofounder and scientific adviser at ideas42, a social enterprise that applies behavioural science to social problems. He is also a recipient of the MacArthur Foundation "Genius Grant", and co-wrote Scarcity: Why Having Too Little Means So Much (Allen Lane) with Eldar Shafir, out October 2013.

This article was first published in the October 2013 issue of WIRED magazine